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commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world.
That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and
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Follow the Tweets.

Every new command is wrapped in a tweet and posted
to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning,
there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

This version handles newlines and other whitespace correctly, the original has problems with the thankfully rare case of newlines in the file names.

It also allows checking an arbitrary number of directories against each other, which is nice when the directories that you think might have duplicates don't have a convenient common ancestor directory.

The lastb command presents you with the history of failed login attempts (stored in /var/log/btmp). The reference file is read/write by root only by default. This can be quite an exhaustive list with lots of bots hammering away at your machine. Sometimes it is more important to see the scale of things, or in this case the volume of failed logins tied to each source IP.

The awk statement determines if the 3rd element is an IP address, and if so increments the running count of failed login attempts associated with it. When done it prints the IP and count.

The sort statement sorts numerically (-n) by column 3 (-k 3), so you can see the most aggressive sources of login attempts. Note that the ':' character is the 2nd column, and that the -n and -k can be combined to -nk.

Please be aware that the btmp file will contain every instance of a failed login unless explicitly rolled over. It should be safe to delete/archive this file after you've processed it.

This sorts files in multiple directories by their modification date. Note that sorting is done at the end using "sort", instead of using the "-ltr" options to "ls". This ensures correct results when sorting a large number of files, in which case "find" will call "ls" multiple times.

sort is way slow by default. This tells sort to use a buffer equal to half of the available free memory. It also will use multiple process for the sort equal to the number of cpus on your machine (if greater than 1). For me, it is magnitudes faster.

If you put this in your bash_profile or startup file, it will be set correctly when bash is started.